Claude Mythos 5.1
Same weights as Fable 5.1, fewer safeguards. Restricted to cyberdefenders and life scientists via trusted access.
Claude Mythos 5.1 · shipped Sep 1, 2026
Mythos Builds on X
The restricted Mythos-class line: Mythos 5.1, Claude Security on Mythos 5, and open reconstructions people actually posted. 4 builds on this page.
Claude Security on Mythos 5
Claude Security scans now run on Mythos 5. Public beta for Claude Enterprise. First-party.
Mythos cryptographic weaknesses
Mythos Preview found new attacks on HAWK and a reduced AES. First-party research from Anthropic.
OpenMythos
A from-scratch PyTorch reconstruction of what Claude Mythos might look like. Looped transformer, MoE, MIT.
